Method of manufacturing semi-fabricated products of chrome-nickel steels



United I StatesPatent O 3,334,999 METHOD OF MANUFACTURING SEMI-FABRI-CATED PRODUCTS OF CHROME-NICKEL STEELS Gerhard Naeser, Duisburg,Germany, assignor to Mannesmann Aktiengesellschaft, Dusseldorf, Germany,a corporation of Germany N Drawing. Filed Feb. 25, 1964, Ser. No. 347,12Claims. (Cl. 75-201) The invention relates to the manufacture bypress-ureforming of sheet metal, wires or tubes, or the like, fromchrome-nickel steel powder; and relates more particularly to suchmanufacture from powder obtained by the atomization with pressure waterfrom a chrome-nickel steel melt.

It is known that the manufacture of semi-fabricated products of sheetmetal, metal bands, wires, or tubes in accordance with existing powdermetallurgical methods, can be economical only if it results in a raisedoutput and quality as compared to the normal manufacture methods forsuch products from starting materials obtained by melting techniques.

It had been proposed to manufacture semi-fabricated products frompowdered steel alloys with a high chrome content or chrome-nickelcontent, the powder being obtained by atomization of a melt withpressure water. It was found, however, that the oxygen absorption of thesteel powder upon its atomization is very high, in fact so high that itrequires a reduction annealing with pure hydrogen. This treatment,however, is so expensive as to render this method uneconomical.

Another proposal, namely to carry out the atomization under theprotective shield of inert gases has, for the same reason, proved to beuneconomical.

It is accordingly among the principal objects of the invention to avoidthe drawbacks of the prior art, and to provide for the economicalmanufacture of semi-fabricated quality products from chrome-nickel steelpowder.

It is a further object of the invention to preoompress the powder thathas predetermined carbon and oxygencontents, and to anneal or sinter theprecompressed articles subsequently in a vacuum whilesimultaneously-decarbonizing and tie-oxidizing the articles, andthereafter to subject them to pressure forming.

Further objects and advantages of the invention will be set forth inpart in the following specification and in part will be obvioustherefrom without being specifically referred to, the same beingrealized and attained as pointed out in the claims hereof.

The foregoing aims, and particularly the aim of improved quality, andstill more particularly of high economy, for manufacturingsemi-fabricated products powdermetallurgically broadly may be realizedin accordance with the instant invention as follows: The chrome-nickelsteel powder may be obtained by atomization from a melt, and may containequivalent amounts of carbon and oxygen; the powder is firstpre-compressed into porous pressed articles such as bands, and thesearticles thereafter are annealed or sintered in a vacuum whilesimultaneously being decarbonized and de-oxidized, and subsequentlythese articles are rolled or pressed.

In order to adjust the stoichiometrical relation of the carbon andoxygen contents of the steel powder, the invention provides for addingto the chrome-nickel-steel melt before the atomization an amount of fromabout .3 to about 1.0 percent carbon. The addition of the carbon effectsa decrease in the oxygen absorption while the metal is in the meltstage, as well as during atomization. This addition of carbon inaccordance with the invention must be sufficiently large, so that duringthe subsequent vacuum annealing of the pre-compressed articles carbonand oxy- 3,334,990 Patented Aug. 8, 1967 ICC gen are removed entirely inthe form of carbon oxide.

The stoichiometrical relation between the carbon and the oxygen may alsobe adjusted by mixing various types of steel powders having diiferentcarbon contents and oxygen contents and, if desired, admixing theretographite powder and/ or powdered oxides such as chromic oxide.

The chrome-nickel steel powder which has thus been obtained, byatomization with pressure water, in spite of its high carbon content andoxygen content lends itself surprisingly well to the formation intopressed articles, such as by rolling into porous bands or, by pressing,into blooms for the subsequent manufacture of tubes.

After the annealing of the aforesaid pressed articles in a vacuum, whichis a good deal less expensive than the annealing in pure hydrogen of theprior art as mentioned, there are obtained carbon contents of below .002percent, which heretofore had been unattainable for objects made ofchrome-nickel steel.

The further working of the annealed or sintered pressed articles intofinished articles, may subsequently be carried out in accordance withwell-known methods, such as rolling or pressing, either hot or cold.

Example A melt on one metric ton of a steel alloy having 18 percentchrome and 8 percent nickel, the carbon content of which had beenincreased by the addition of graphite to .6 percent, was atomized withpressure water having a pressure of 60 atmospheres excess pressure(atii), in 3 minutes, into a steel powder having a particle size of lessthan .5 mm. The oxygen content of the steel .powder amounted to .9percent. The stoichiometrical relation between the carbon content andthe oxygen content was adjusted by mixing the powder obtained with adifferent steel powder that had a higher oxygen content. The resultantmixture was formed into a porous band of a thickness of 4 mm., which wasthen rolled up on a reel and annealed for two hours in a vacuum of .3mm. mercury at a temperature of 1170 C. This caused the carbon contentto be lowered from .6 percent to .002 percent, and the oxygen content tobe lowered to .06 percent. The annealed and sintered band subsequentlywas subjected to hot rolling. It showed thereafter excellent strengthproperties which were equivalent to those of steel bands made inaccordance with the usual normal rolling process.

I wish it to be understood that I do not desire to be limited to'theexact details of construction shown and described, for obviousmodifications will occur to a person skilled in the art.

Having thus described the invention, what I claim as new and desire tobe secured by Letters Patent, is as follows:

1. In a method of manufacturing semi-fabricated products, such as sheetmetal, wires or tubes, the steps comprising, preparing a chrome-nickelsteel melt, atomizing said melt with pressure water thereby obtaining achrome-nickel steel powder, pre-compressing said powder into porouspressed articles, subsequently sintering said articles in a vacuum at atemperature above 1000 C. for a period in excess of one hour, whilesimultaneously decarbonizing and deoxidizing said articles andthereafter subjecting them to pressure forming of the rolling and,respectively, pressing type.

2. In a method of manufacturing semi-fabricated products, as claimed inclaim 1, and adjusting the stoichiometrical relation between the carboncontent and the oxygen content of the powder by the mixing, into amixture, of various types of chrome-nickel steel powders havingdifferent carbon contents and oxygen contents.

3. In a method of manufacturing semi-fabricated products, as claimed inclaim 2, and admixing to said mixture at least one powder taken from agroup of powders, consisting of graphite powder and oxide powder.

4. In a method of manufacturing semi-fabricated products, as claimed inclaim 3, said oxide powder being chromic oxide powder.

5. In a method of manufacturing semi-fabricated products, such as sheetmetal, wires, or tubes, of chromenickel steel, the steps comprising,preparing a chromenickel steel melt, atomizing said melt with pressureWater thereby obtaining a chrome-nickel steel powder, adjusting thestoichiometrical relation between the carbon content and the oxygencontent of said powder by adding to the melt, prior to the atomization,of from about .3 to about 1.0 percent carbon, pro-compressing saidpowder into porous pressed articles, subsequently sintering saidarticles in a vacuum at a temperature above 1000 C. for a period inexcess of one hour while simultaneously decarbonizing and deoxidizingsaid articles and thereafter subjecting them to pressure forming of therolling and, respectively, pressing type.

References Cited UNITED STATES PATENTS OTHER REFERENCES Cox, Vacuumsintering, Metal Industry, Sept. 16, 1960.

'CARL D. QUARFORTH, Primary Examiner.

BENJAMIN R. PADGETT, Examiner. A. J. STEINER, Assistant Examiner.

1. IN A METHOD OF MANUFACTURING SEMI-FABRICATE PRODUCTS, SUCH AS SHEETMETAL, WIRES OR TUBES, THE STEPS COMPRISING, PREPARING A CHROME-NICKELSTEEL MELT, ATOMIZING SAID MELT WITH PRESSURE WATER THEREBY OBTAINING ACHROME-NICKEL STEEL POWER, PRE-COMPRESSING SAID POWDER INTO POROUSPRESSED ARTICLES, SUBSEQUENTLY SINTERING SAID ARTICLES IN A VACUUM AT ATEMPERATURE ABOVE 1000* C. FOR A PERIOD IN EXCESS OF ONE HOUR, WHILESILULTANEOUSLY DECARBONIZING AND DEOXIDIZING SAID ARTICLES ANDTHEREAFTER SUBJECTING THEM TO PRESSURE FORMING OF THE ROLLING AND,RESPECTIVELY, PRESSING TYPE.